This invention pertains generally to apparatus for optical measurements and particularly to optical interferometers.
It has been standard practice in the art for many years to determine the optical quality of mirrors by utilizing the principles of interference in the design and operation of optical measuring equipment. Thus, it is well known to provide instrumentation whereby a beam of light may be divided into two parts which are caused to traverse different optical paths (sometimes referred to hereinafter, respectively, as the reference path and the test path) and then are caused to be reunited. The interference pattern between the parts making up the reunited beam, then, is an indication of any difference between the reference path and the test path. If, therefore, a mirror to be tested is placed in an appropriate test path, the resulting interference pattern observed on a viewing screen may be taken as an indication of the optical quality, i.e. the smoothness and shape, of such mirror.
While instrumentation of the type being discussed is of practical use for determining the optical quality of many different kinds of mirrors, limitations exist which detract substantially from the value of such instrumentation. That is to say, in addition to the requirement (common to any optical instrumentation) that the elements of any optical interferometer be fabricated and positioned with an extremely high degree of precision, the optical quality of only a relatively small area on a mirror to be tested may be determined at any given time. Such an areal limitation makes the determination of the optical quality of a planar mirror of any substantial size a most difficult, tedious and time-consuming undertaking and the determination of the optical quality of a curved mirror an almost impossible task.